Lest anyone get the wrong impression, all of our applications were specifically designed to preserve your ability to access your data. They store their data in a format called XML.
XML's an
open standard. We don't own it and never could. It's also a format that's designed to make data accessible and human-readable whenever possible. It's about as un-proprietary as you can get. An XML file is just plain text; all the OmniFocus-specific stuff is just sequences of extra characters wrapped around your content that tells OmniFocus how to process it.
OmniFocus' use of XML is one of the reasons why a service like
Spootnik can exist. The author of that service didn't get any special help from us; presumably, he looked at his OmniFocus database, figured out how it worked, and then hooked that up to
Basecamp.
By contrast, until very recently Microsoft was
notorious for having all their apps use file formats that weren't documented or accessible to third parties. They started changing that, but only after getting hit over the head with several anti-trust lawsuits...
That said, Gareth, I totally hear and understand the underlying concern/desire. Outlook is pretty ubiquitous among some circles; that's a good reason to want OmniFocus to talk to it. Ubiquity doesn't make it any less proprietary, though. :-)